AUGITE

The
Pyroxene Group
of Minerals


AEGIRINE


DIOPSIDE


HEDENBERGITE


SPODUMENE

 

The pyroxene minerals are inosilicates of the general formula XY(Si, Al)2O6. The X, represents ions such as calcium, sodium, iron+2 and magnesium and more rarely zinc, manganese and lithium. The Y, represents ions of generally smaller sized such as chromium, aluminum, iron+3, magnesium, manganese, scandium, titanium, vanadium and even iron+2. Aluminum, while commonly substituting for silicon in other silicates, does not often substitute for silicon in a pyroxene.

The typical pyroxene structure contains chains of SiO3 tetrahedrons that every other one alternates from the left side to the right side of the chain. Each of the tetrahedrons has one flat edge that lies on the "base" of the structure as if the entire chain were a chain of connected three sided pyramids on a flat desert. The orderliness of the tetrahedrons means that they repeat every three tetrahedrons, ie. left-right-left. The chain structure explains the general prismatic to fibrous character of the members of this group. The slope of the tetrahedral pyramids helps to determine the cleavage angle of the pyroxenes at nearly 90o degrees (actually 93o and 87o).

The pyroxenes are closely related to a group of inosilicates called the pyroxenoids. This somewhat informal group of minerals has a similar chain structure but the chains in the pyroxenoid structures are more . . . "kinked"!

The pyroxenes are an important group among the single chained inosilicates. They are common rock forming minerals and are represented in most igneous and many metamorphic rocks. Their presence in a rock indicate a high temperature of crystallization with a lack of water. If water were present, a double chained amphibole would most likely have formed instead. The name pyroxene comes from the Greek words for fire and stranger in a false allusion to their surprising presence in volcanic lavas. Pyroxenes are sometimes seen as crystals embedded in volcanic glass and the assumption was that they are impurities in the glass, hence the term "fire strangers". However the pyroxenes are simply early forming minerals that crystallized before the lava erupted.


These are the members of the Pyroxene Group:

    Clinopyroxenes (monoclinic)

    • Aegirine (Sodium Iron Silicate)
    • Augite (Calcium Sodium Magnesium Iron Aluminum Silicate)
    • Clinoenstatite (Magnesium Silicate)
    • Diopside (Calcium Magnesium Silicate)
    • Esseneite (Calcium Iron Aluminum Silicate)
    • Hedenbergite (Calcium Iron Silicate)
    • Hypersthene (Magnesium Iron Silicate)
    • Jadeite (Sodium Aluminum Silicate)
    • Jervisite (Sodium Calcium Iron Scandium Magnesium Silicate)
    • Johannsenite(Calcium Manganese Silicate)
    • Kanoite (Manganese Magnesium Silicate)
    • Kosmochlor (Sodium Chromium Silicate)
    • Namansilite (Sodium Manganese Silicate)
    • Natalyite (Sodium Vanadium Chromium Silicate)
    • Omphacite (Calcium Sodium Magnesium Iron Aluminum Silicate)
    • Petedunnite (Calcium Zinc Manganese Iron Magnesium Silicate)
    • Pigeonite (Calcium Magnesium Iron Silicate)
    • Spodumene (Lithium Aluminum Silicate)

    Orthopyroxenes (Orthorhombic)

    • Donpeacorite (Manganese Magnesium Silicate)
    • Enstatite (Magnesium Silicate)
    • Ferrosilite (Iron Magnesium Silicate)
    • Nchwaningite (Hydrated Manganese Silicate)
Popular Members of the Silicates Class












 

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